The invention is directed to an alkaline bath for the electrolytic deposition of low carat rose to yellow colored gold alloy coatings containing soluble gold cyanide, soluble copper cyanide, and potassium carbonate or potassium bicarbonate. Thereby there are deposited corrosion resistant coatings in the range of 13 to 18 carats.
For the production of low carat rose and yellow colored gold alloy coatings there have previously been used baths which contain besides complex gold and copper cyanides, cadmium and chelate formers (German OS 2221159, the entire disclosure of which is hereby incorporated by reference and relied upon). Such baths generally operate in a pH range of 7.5 to 12 and contain besides cyanide, conductive salts such as carbonates and buffer salts such as e.g., phosphates. They produce, with favorable operating conditions, glossy rose colored or yellow alloy precipitates of good quality. However, these baths have the serious disadvantage that they contain cadmium which is physiologically hazardous and must be replaced by other materials.
There are also known gold baths which contain, as soluble salts, besides gold also zinc and other alloying metals, especially copper. However, until now with such electrolytic baths, there have been produced no rose colored or yellow low carat gold alloy coatings, but only high carat or discolored coatings.
In German OS 2342691 there is described an alkaline cyanidic white gold bath which, besides potassium gold cyanide and potassium zinc cyanide, contains potassium nickel cyanide and dipotassium hydrogen phosphate at a pH of 9-13. However, with these baths there cannot be produced low carat gold alloy coatings.
There is known from German OS 2244434 an electrolytic gold alloy bath which besides potassium gold cyanide, also contains copper sulfate and, in a given case, a zinc salt. However, there are not obtained from these baths which operate at a pH of 3-10 and contain aldehyde, diamine and arsenious acid as essential components any low carat gold alloy layers.
In German OS 2754207 there is described a gold alloy bath which contains potassium gold cyanide, zinc sulfate and sodium carbonate and is operated at a pH of 4.9. There are deposited from this bath green precipitates.
Furthermore, there is known (German AS 1033987) a gold alloy bath which contains potassium gold cyanide, copper, zinc and nickel in the form of their ethylenediamine tetraacetic acid salts. There are obtained at a pH of 8 and a temperature of 60.degree. C. 19 carat alloy coatings which are greyish.
With none of the electrolytic gold alloy baths mentioned here based on gold, copper, zinc, was it possible until now to produce low carat rose to yellow colored coatings.
Therefore, it was the problem of the present invention to develop an alkaline bath for the electrolytic deposition of low carat rose to gold colored gold alloy coatings containing soluble gold cyanide, soluble copper cyanide, and potassium carbonate or potassium bicarbonate which produce corrosion resistant, physiologically safe 13-18 carat coatings.